Seasonal food web models for the Oregon inner-shelf ecosystem : investigating the role of large jellyfish

Abstract/OtherAbstract
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Previously published in California Cooperative Oceanic Fisheries Investigations Progress Report, 2007, Vol.48; access courtesy of publisher and authors., We developed two seasonal food-web models, spring
and summer, within the Ecopath framework for the
Oregon upwelling ecosystem to investigate the role of
large jellyfish as competitors for zooplankton prey. We
used information about fish and jellyfish biomass, distribution,
and diet derived from pelagic trawl survey
data. Information about lower trophic-level production
was acquired from zooplankton survey data. The models
indicate that in spring, jellyfish are a modest consumer
of zooplankton, and forage fishes dominate the
system in terms of biomass and consumption. By late
summer, jellyfish become the major zooplankton consumers,
and they consume 17% of the summer zooplankton
production while forage fish consume 9%.
Jellyfish appear to divert zooplankton production away
from upper trophic levels. Only 2% of the energy consumed
by jellyfish is passed to higher trophic levels.
However, the role of jellyfish as competitors may be
moderate; a large proportion of zooplankton production
(40%–44%) is not consumed but lost to detritus.